Bring a large pot of salted water to a rolling boil, then add the tri-color rotini pasta. Cook according to package instructions until al dente, about 8-10 minutes. Drain and rinse under cold water until cooled to room temperature.

In a spacious mixing bowl, combine the quartered cherry tomatoes, sliced pepperoni, finely chopped red onion, diced green bell pepper, cubed mozzarella cheese, grated Parmesan cheese, and sliced olives. Fold together gently.

In a separate bowl, whisk together olive oil, red wine vinegar, Italian seasoning, garlic powder, salt, and pepper. Add a pinch of red pepper flakes if desired.

Pour the vinaigrette over the pasta and vegetable mixture. Toss gently until every component is evenly coated.

Cover the mixing bowl or transfer salad to an airtight container. Refrigerate for at least 1 hour to allow flavors to meld.

Remove from the fridge, let sit for about 20-30 minutes at room temperature before serving. Refresh dressing with olive oil and vinegar if necessary.